1. Field of the Invention
The present invention relates to a telecommunications control device, and more particularly to a telecommunications control device applicable to a telecommunications network system, such as a sensor network, a wireless ad hoc network, a local area network (LAN), or other kinds of network, including a plurality of nodes dispersedly disposed or mounted on mobile bodies to send data to each other while avoiding a collision of data due to radio interference, etc. The present invention also relates to a telecommunications control method therefor.
2. Description of the Background Art
A method of avoiding a collision of data by allowing each of a plurality of nodes to adjust its own transmission timing autonomously without resorting to a central administrative server is disclosed by U.S. patent application publication Nos. US 2005/0190796 A1 to Date et al., US 2006/0050826 A1 to Date et al., US 2006/0114841 A1 to Date et al., US 2006/0114840 A1 to Date et al., US 2006/0171409 to Date et al., and US 2006/0171421 A1 to Matsunaga et al., by way of example.
In the telecommunications control devices and methods taught in the six patent publications set forth above, each node transmits and receives an impulse signal, which is a control signal indicative of the data transmission timing of its own node, periodically to and from its neighboring nodes, thereby adjusting its own transmission timing mutually. This enables an autonomous time slot allocation. More specifically, the time interval of one period (transmission period of an impulse signal) is divided into time slots, which are allocated to nodes lying within a signal range in which impulse signals can be transmitted and received. Note that an impulse signal does not always need to be formed in the form of impulse-shaped signal. It may be constituted by packets etc., as with control signals. Hence, an impulse signal is also called a timing control signal. The transmission period of a timing control signal will hereinafter be referred to simply as a period. The range of a timing control signal transmitted by each node corresponds to an interaction range in which that node performs an adjustment of transmission timing.
There are several solutions of transmitting and receiving a timing control signal between neighboring nodes. In the first solution, as shown in FIG. 2A, nodes, e.g. a node i of interest, are arranged to have the signal range Ci thereof within which the timing control developed therefrom is available broader than the signal range Di within which a data signal developed therefrom is available. For instance, the former may be set about twice as broad as the latter by adjusting the ratio in transmission power of a timing control signal to a data signal. That intends to avoid a collision of data that would otherwise occur due to a hidden node, etc.
In the second solution, as shown in FIG. 2B, nodes, e.g. a node of interest i, have the timing control signal range Ci and data signal range Di thereof formed the same, i.e. the same in transmission power, and the node of interest generates a virtual phase with respect to another node, corresponding to a virtual phase described in the aforementioned '480 Date et al. patent, based on a timing control signal received from the other to transmit the virtual phase along with the timing control signal of the node of interest.
The other node, e.g. a node included in a solid-line circle 21, FIG. 2B, works, when having received a timing control signal from the node of interest i, so as to generate a virtual phase of the own node if not exist within itself, or adjust the value of a virtual phase when already exists. Thereafter, the value of the generated or adjusted virtual phase varies at a constant rate equivalent to the specific angular frequency. Then, the value of the virtual phase of the node of interest at the current time is transmitted when the other node transmits its timing control signal. In this manner, the phase information of the node of interest is transmitted to a third node two hops ahead of the node of interest, e.g. a node 23 lying within the dashed-line circle 25 but not included within the solid-line circle 21 in FIG. 2B, through another node one hop ahead of the node of interest, e.g. a node 27 included within the solid-line circle 21 in FIG. 2B.
While the mechanism of transmitting the phase information of the node of interest to the third node two hops ahead has been described, the phase information of any node can be likewise transmitted to a node two hops ahead. As a result, an interaction range in the transmission timing adjustment is about two hops ahead of each node, as depicted with the circle 25, FIG. 2B.
In the case of transmitting and receiving the above-described timing control signal by the telecommunications control devices and methods disclosed by the six patent publications described above, normally, the smaller the period, the smaller the communication delay.
However, there is a problem that if the period becomes smaller, the ratio of the transmission and reception interval of the timing control signal to the period will increase accordingly, and therefore the transmission efficiency of a data signal will be lowered. Therefore, in order to achieve lower delay and attain higher transmission efficiency, it is vital to make the overhead of the timing control signal as small as possible.